This invention relates to a multi-piece solid golf ball comprising an elastic solid core enclosed with a resin cover of two different hardness layers and exhibiting uniform flight performance.
The golf balls are now under a rapid transition from the thread wound structure to the solid structure because most golfers favor the superior distance performance of solid balls.
The solid structure is initially typified by two-piece solid golf balls in which a solid core of rubber having excellent resilience is disposed at the center of the ball as the majority thereof and enclosed with a hard resin cover formed of ionomer resins or the like for providing protection against external damages.
Although the solid ball is good in distance, it undergoes a smaller deformation upon impact than the wound golf ball. The solid ball then gives a hard or unpleasant feel when hit. Since the smaller deformation corresponds to a smaller area of contact with the club face, the solid ball receives less spin and is thus less controllable on use of an iron club.
Many attempts were made to overcome these drawbacks, for example, by reducing the hardness of the solid core, placing a buffer layer between the core and the cover, and using relatively flexible polyurethane as the cover stock.
As a consequence, the feel and spin rate are improved to a substantially satisfactory level. However, the same attempts for such improvement raise new undesirable issues. Due to a decline of rebound, the distance characteristic of the solid structure is rather reduced. When hit with a wood club, especially a driver intended for distance, the ball receives more spin so that the ball may rather sky, thus traveling a shorter distance. No substantial progress has been marked in solving the above problems.
An object of the present invention is to provide a golf ball comprising a solid core and a plurality of enclosing layers in which the combination of materials of the enclosing layers and the configuration and arrangement of dimples on the outermost enclosing layer or cover are adjusted such that the ball is given both the performances that the ball, when hit with a driver or similar club having a high head speed, may travel a distance while suppressing the reception of excessive spin, and when hit with a short iron or similar club having a large loft angle, may receive a high spin rate, which have been allegedly difficult to achieve both at the same time.
The present invention provides a golf ball comprising an elastic solid core, an intermediate layer around the core, and a resin cover around the intermediate layer, composed mainly of a urethane elastomer and having a plurality of dimples on its surface. The dimples include 330 to 400 circular dimples having a diameter of at least 3.7 mm, have a total volume of 330 to 380 mm3, and are substantially uniformly distributed such that there is no or only one great circle which does not intersect with the dimples. Owing to the optimized shape and arrangement of dimples combined with the inherent advantages of multi-piece solid golf balls, the golf ball has improved travel distance performance and uniform flight performance to ensure a high spin rate on short iron shots.
In a preferred embodiment, SP is in the range of 80 to 94, provided that a sphere consisting of the core and the intermediate layer undergoes a distortion A when the load applied thereto is increased from 98 N (10 kgf) to 1275 N (130 kgf), the intermediate layer has a Shore D hardness B, the cover has a Shore D hardness C and a gage D, and SP is defined as a function of A, B, C and D by the following equation: SP=C+0.5Bxe2x88x925D+5A.
Also preferably, the dimples account for at least 78% of the outer surface area of the ball.